1. Field of the Invention
This invention relates to an air introduction system of a fuel injection type internal combustion engine, more particularly, to an air introduction system in which a part of introduced air, hereinafter referred to as "assist air", is supplied to a top nozzle portion of a fuel injector so as to improve the atomization of injected fuel.
2. Description of the Prior Art
In an air assist system of a fuel injection type engine, assist air which does not pass through a throttle valve is introduced to the surrounding area of a top nozzle portion of a fuel injector. Conventionally the flow of the assist air has been controlled in the following manners. In one of the conventionally known air assist systems, the flow of the assist air is set to be constant so that it conforms to a required flow of air in the idling condition of the engine. In this case, however, there is a problem in that the amount of assist air is insufficient at the transitional or usual driving condition of the engine, and the original purpose of the air assist system, that is, promoting the atomization of injected fuel, cannot fully be attained. According to another conventionally known air assist system, the flow of assist air is controlled by an idling speed controller (ISC) or the like, which, however, makes the whole system complicated and expensive, although the original purpose of the air assist system can be satisfactorily attained.